Exploring N-Heterocyclic Carbene Effects on Hyperpolarisation with para-Hydrogen

This research focuses on the Nuclear Magnetic Resonance (NMR) applications of Signal Amplification by Reversible Exchange (SABRE); a hyperpolarisation technique discovered within the Duckett Group. The hyperpolarisation technique, SABRE, is used to enhance the magnetic resonance signals produced in NMR and improve the resolution seen in an NMR spectrum. Parahydrogen is used as the source of hyperpolarisation. This research aims to focus on developing SABRE techniques by determining the most efficient SABRE-active catalyst which can be further applied to biomedical applications.
SABRE catalysts are made up of an N-heterocyclic carbene ligand and a substrate in a solvent of choice. In 2009, A SABRE-active catalyst with the general formula [Ir(H)2(NHC)(sub)3]Cl, where NHC = N-heterocyclic carbenes, and substrates, were synthesised and used to enhance NMR signals through the hyperpolarisation technique, SABRE. This research aims to investigate different N-heterocyclic ligands and determine the efficiencies of their corresponding SABRE catalysts by determining the largest total signal enhancements produced by these catalysts. The catalysts were characterised by Nuclear Magnetic Resonance (NMR) spectroscopy and Mass Spectrometry (MS). These catalysts were further examined to determine their optimum environment as signal enhancement is dependent on various properties such as; substrate concentration, temperature and solvent. The rates of substrate exchange at the catalyst were also determined to establish the optimum conditions.
As SABRE can be applied to biomedical applications, two biological molecules were used as the substrates throughout this research and these were pyridine and a pyridine derivative, 3-5-Lutidine. The 1H NMR signals of pyridine and 3,5-lutidine were shown to be enhanced using SABRE, a non-hydrogenative parahydrogen induced polarisation (PHIP) application.
Work has previously looked at different NHC and substrate combinations that produce the largest total signal enhancements and by optimisation of the conditions and NHC, a 5500-fold total pyridine signal enhancements was discovered when the NHC was IMes, 1,3-bis(2,4,6-trimethylphenyl)-imidazol-2-ylidene